Wobble signal extraction circuit and optical disk device

ABSTRACT

A wobble signal extraction circuit for extracting a wobble signal from a first optical disk signal containing a wobble signal component caused by a wobble formed on a surface of an optical disk and a second optical disk signal containing a wobble signal component of a reversed phase to that of the first optical disk signal, wherein signal level fixing sections ( 24   a  and  24   b ) fix the first and second optical disk signals to a predetermined level when a discontinuity of the wobble is detected.

TECHNICAL FIELD

The present invention relates to a technique for recording/reproducinginformation to/from an optical disk to/from which information can beoptically recorded/reproduced, and more particularly to a circuittechnique for use in an optical disk apparatus for spinning an opticaldisk and obtaining track position information based on a wobble formedon the surface of the optical disk, by which a wobble signal caused bythe wobble is accurately extracted from a signal reproduced from theoptical disk.

BACKGROUND ART

A conventional optical disk apparatus records/reproduces data to/from anoptical disk while performing a tracking operation based on a guidegroove that is formed in advance on the surface of the optical disk soas to be winding in the radial direction, i.e., a wobble. FIG. 6 shows aconfiguration of a CD-R recording/reproduction apparatus as an exampleof a conventional optical disk apparatus. An optical pickup 100irradiates an optical disk 101 being spun at a certain speed with laserlight, and the reflected light is detected by a divided photodetectorand converted into an electric signal. For the obtained signal, a servosignal producing circuit 102 produces a focus and tracking error signalto perform a focus and tracking servo control of the optical pickup 100through a servo controller 103.

FIG. 7 is a diagram showing on an enlarged scale the surface of theoptical disk 101 under a servo control. Under a servo control, laserlight output from the optical pickup 100 is condensed into a spot asshown by a laser spot 110, and the spot is controlled by a trackingcontrol so as to be always along a guide groove 111. If information isrecorded on the optical disk 101, there are pits 112 along the guidegroove 111, and the optical pickup 100 produces a signal based on thereflected light whose intensity changes depending on thepresence/absence of the pits 112.

Referring back to FIG. 6, a wobble signal extraction circuit 104extracts a wobble signal caused by the guide groove 111 shown in FIG. 7,i.e., a wobble. The servo controller 103 performs a spindle servocontrol by controlling the rotational speed of a spindle motor 105 sothat the frequency of the wobble signal becomes equal to an intendedvalue. Absolute time information (ATIP: Absolute Time In Pre-groove)that indicates address information of the optical disk 101 is embeddedin the wobble signal. An ATIP decoder 106 decodes ATIP from the wobblesignal, and sends, to a CPU 107, position information of the opticalpickup 100 in the optical disk 101. A data signal producing circuit 108produces a data signal from the signal produced by the optical pickup100. A decoder 109 decodes the data signal produced by the data signalproducing circuit 108 to decode the signal recorded on the optical disk101.

The wobble signal extraction circuit 104 of the above optical diskapparatus will now be described in detail. FIG. 8 shows a configurationof the conventional wobble signal extraction circuit 104. The wobblesignal extraction circuit 104 receives, from the optical pickup 100,optical disk signals S1 and S2 containing an RF signal component being adata reproduction signal and a wobble signal component caused by awobble formed on the optical disk 101, and subtracts, at a subtracter120, the optical disk signal S2 from the optical disk signal S1 toextract a wobble signal.

FIG. 9 show diagrams for illustrating the principle of the wobble signalextraction operation performed by the wobble signal extraction circuit104. When reproducing a recorded optical disk, light 130 is ideallyreflected off the disk surface equally by portions A, B, C and D of aphotodetector 131, as shown in FIG. 9(a). Then, an A+D signal producedfrom the portions A and D arranged next to each other in the diskrotation direction (i.e., the optical disk signal S1 shown in FIG. 8)and a B+C signal produced from the portions B and C similarly arrangednext to each other in the disk rotation direction (i.e., the opticaldisk signal S2 shown in FIG. 8) have RF signal components of the samephase and of the same amplitude, and have wobble signal components ofreversed phases and of the same amplitude. Therefore, by subtracting theoptical disk signal S2 from the optical disk signal S1 with thesubtracter 120 shown in FIG. 8, the RF signal components contained inthese signals are canceled out, whereby an (A+D)−(B+C) signal thatcontains only the wobble signal component can be extracted as the outputsignal of the subtracter 120.

However, due to factors such as the limit on the precision in theplacement of the photodetector 131 when manufacturing an optical diskapparatus, light 130′ is reflected asymmetrically with respect to thephotodetector 131 as shown in FIG. 9(b). Then, the RF signal componentsand the wobble signal components contained in the A+D signal and the B+Csignal will be of different amplitudes. In view of this, the opticaldisk signals S1 and S2 are passed to the subtracter 120 after beingadjusted through automatic gain controllers (hereinafter referred to as“AGC circuits”) 121 and 122 so that they will have the same amplitude.Moreover, an RF signal component remaining in the output from thesubtracter 120 is removed by a bandpass filter 123, thus extracting awobble signal S3. Then, the extracted wobble signal S3 is digitized by adigitizer circuit 124, and is used as a clock in the optical diskapparatus for a spindle servo control and for obtaining disk addressinformation (see, for example, Patent Document 1).

Optical disks currently available in the market include WORM-typeoptical disks including DVD-R in addition to CD-R, and rewritableoptical disks such as CD-RW, DVD-RAM and DVD-RW. Arecording/reproduction apparatus compatible with these optical disksalso extracts a wobble signal from an optical disk in a manner similarto that described above to produce a necessary clock signal whenrecording data.

(Patent Document 1) Japanese Laid-Open Patent Publication No. 8-194969

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

A land/groove recording method is employed for DVD-RAM disks. In theland/groove recording method, address information are arranged in astaggered pattern along the track of a land portion and along the trackof a groove portion. Therefore, the wobble signal will not be acontinuous signal, but is cut off when reading a CAPA (ComplimentaryAllocated Pit Addressing) portion. Therefore, when reading a CAPAportion, i.e., when the output laser light moves from a DATA portioninto a CAPA portion or from a CAPA portion into a DATA portion, the DClevel and the amplitude of the optical disk signals input to thesubtracter 120 shown in FIG. 8 may vary rapidly to exceed the acceptableinput amplitude range of the subtracter 120, thus saturating thesubtracter 120. In this case, it requires some time after the readposition moves into a DATA portion and before the subtracter 120recovers from the saturated state back to the normal state, and theresponse characteristics of the subtracter 120 during this recoveryperiod will be different from those in the normal state.

With DVD-R/RW, when reading a land pre-pit area on the disk surface, aland pre-pit signal is superimposed on the RF signal. Therefore, as withDVD-RAM, the amplitude level of the signal input to the subtracter 120or the AGC circuits 121 and 122 shown in FIG. 8 may vary rapidly toexceed the acceptable input amplitude range of the circuit.

In a case where the AGC circuits 121 and 122 are provided preceding thesubtracter 120 as shown in FIG. 8, one of the two optical disk signalsoutput from the photodetector will be missing when reading a CAPAportion, whereby the AGC circuit for which the signal is missing may besaturated.

A countermeasure to the problem above is to set the acceptable inputamplitude range of the subtracter 120 to be sufficiently large in viewof the DC variation and the amplitude variation. However, this isdisadvantageous in terms of the power consumption of the circuit and thecircuit area. Even if an HPF (high-pass filter) is provided along a pathextending from the light-receiving portion to the subtracter 120, the DCvariation cannot be removed since it is a frequency component close tothe RF band. Thus, a wobble signal extraction circuit of a CD-R/RWrecording/reproduction apparatus is not compatible with DVD-RAM/R/RW,and if it is used with DVD-RAM/R/RW, a wobble signal cannot be obtainedstably. Therefore, in order to realize an optical disk apparatuscompatible with both CD-R/RW and DVD-RAM/R/RW, it is necessary toimplement two different wobble signal extraction circuits. However, thisis disadvantageous in terms of the circuit area.

In view of the above, it is an object of the present invention torealize a wobble signal extraction circuit and an optical disk apparatuscompatible with various types of optical disks and capable of stableextraction of a wobble signal while suppressing an increase in thecircuit scale and power consumption.

MEANS FOR SOLVING THE PROBLEMS

In order to solve the problems above, the present invention provides awobble signal extraction circuit for extracting a wobble signal from afirst optical disk signal containing a wobble signal component caused bya wobble formed on a surface of an optical disk and a second opticaldisk signal containing a wobble signal component of a reversed phase tothat of the first optical disk signal, including first and second signallevel fixing sections for fixing the first and second optical disksignals, respectively, to a predetermined level when a discontinuity ofthe wobble is detected.

With this invention, the first and second optical disk signals are fixedto a predetermined level by first and second signal level fixingsections when a discontinuity of the wobble is detected. Therefore,signals exceeding an acceptable input amplitude range will not be inputto a circuit that receives the first and second optical disk signals,e.g., a subtracter, whereby the circuit can have a relatively smallacceptable input amplitude range.

Preferably, the wobble signal extraction circuit includes first andsecond normalizer sections for adjusting amplitudes of the first andsecond optical disk signals, respectively, to a predetermined magnitude.The first and second signal level fixing sections are provided precedingthe first and second normalizer sections, respectively.

Preferably, the wobble signal extraction circuit includes a gainadjustment section for, when the first and second optical disk signalsare fixed to the predetermined level respectively by the first andsecond signal level fixing sections, fixing gains of the first andsecond normalizer sections to a value used immediately before the firstand second optical disk signals are fixed to the predetermined level, orto a predetermined value.

Preferably, the first and second signal level fixing sections perform asample-and-hold operation on the first and second optical disk signals,respectively, and hold the first and second optical disk signals to thepredetermined level when the discontinuity of the wobble is detected.

In order to solve the problems above, the present invention alsoprovides a wobble signal extraction circuit for extracting a wobblesignal from a first optical disk signal containing a wobble signalcomponent caused by a wobble formed on a surface of an optical disk anda second optical disk signal containing a wobble signal component of areversed phase to that of the first optical disk signal, including: asubtracter for subtracting the second optical disk signal from the firstoptical disk signal; and a signal level fixing section for fixing anoutput signal of the subtracter to a predetermined level when thediscontinuity of the wobble is detected.

With this invention, the output signal of the subtracter is fixed to apredetermined level by the signal level fixing section when adiscontinuity of the wobble is detected. Therefore, signals exceeding anacceptable input amplitude range will not be input to a circuit thatreceives the output signal of the subtracter, e.g., a bandpass filter,whereby the circuit can have a relatively small acceptable inputamplitude range.

In order to solve the problems above, the present invention alsoprovides a wobble signal extraction circuit for extracting a wobblesignal from a first optical disk signal containing a wobble signalcomponent caused by a wobble formed on a surface of an optical disk anda second optical disk signal containing a wobble signal component of areversed phase to that of the first optical disk signal, including: asignal switcher for selectively outputting one of the first and secondoptical disk signals; and a subtracter for subtracting a signal outputfrom the signal switcher from the first optical disk signal. The signalswitcher outputs the first optical disk signal when the discontinuity ofthe wobble is detected.

With this invention, when a discontinuity of the wobble is detected, thefirst optical disk signal is output from the signal switcher, wherebythe two inputs to the subtracter will be of the same value and thus willbe canceled out. Therefore, the subtracter can have a relatively smallacceptable input amplitude range.

Specifically, the optical disk is in compliance with the DVD-RAMstandard or the DVD-R/RW standard, and the discontinuity of the wobbleis a CAPA portion or a land pre-pit area.

EFFECTS OF THE INVENTION

As described above, according to the present invention, a wobble signalcan be stably extracted with a single wobble signal extraction circuitfor various types of optical disks. Thus, the circuit area is reduced ascompared with conventional examples where two different wobbleextraction circuits are provided. Moreover, the acceptable inputamplitude range required for each circuit is suppressed to be small,thereby allowing for an operation with a low power consumption and a lowpower supply voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of an optical disk apparatusaccording to a first embodiment of the present invention.

FIG. 2 is a diagram showing an optical disk signal when reading a CAPAportion of a DVD-RAM.

FIG. 3 is a diagram showing a configuration of an optical disk apparatusaccording to a second embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of an optical disk apparatusaccording to a third embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of an optical disk apparatusaccording to a fourth embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a conventional opticaldisk apparatus.

FIG. 7 is an enlarged view of a surface of an optical disk under a servocontrol.

FIG. 8 is a diagram for illustrating a principle of a wobble signalextraction operation performed by a wobble signal extraction circuit.

FIG. 9 shows graphs each showing the relationship between an extractedwobble signal and a signal obtained by digitizing the extracted wobblesignal.

BEST MODE FOR CARRYING OUT THE INVENTION

Best modes for carrying out the present invention will now be describedwith reference to the drawings. Reference numerals used in the drawingsinclude the following.

-   24, 24 a, 24 b Signal level fixing section-   26 a, 26 b Normalizer section-   27 a, 27 b Gain adjustment section-   28 Signal switcher-   23 Subtracter

First Embodiment

FIG. 1 shows a configuration of an optical disk apparatus according to afirst embodiment of the present invention. The optical disk apparatus ofthe present embodiment includes a photodetector 20, adder circuits 21and 22, signal level fixing sections 24 a and 24 b, a subtracter 23 anda bandpass filter 25. The wobble signal extraction circuit of thepresent embodiment is a portion including the adder circuits 21 and 22,the signal level fixing sections 24 a and 24 b, the subtracter 23 andthe bandpass filter 25.

Signals obtained by detecting reflected light from an optical disk atportions of the 4-part photodetector 20 are referred to as optical disksignals A, B, C and D. These signals are signals that are read by thephotodetector 20 after the photodetector 20 is placed under a trackingand focus servo control so that data can be recorded/reproduced to/froman optical disk, and are signals each obtained by synthesizing an RFsignal component and a wobble signal component. From these optical disksignals A to D, the adder circuits 21 and 22 produce a sum signal (A+D)(corresponding to the first optical disk signal) for the inner peripheryside of the disk and a sum signal (B+C) (corresponding to the secondoptical disk signal) for the outer periphery side of the disk. Then, thesubtracter 23 subtracts the sum signal (B+C) from the sum signal (A+D),thus removing the RF signal component contained in the two sum signalsand extracting the wobble signal. Then, the bandpass filter 25 extractsan intended frequency component from the differential signal(A+D)−(B+C). The wobble signal extraction circuit of the presentembodiment will now be described with reference to the case of DVD-RAM.

In a DVD-RAM, CAPA portions 113 each representing address informationare arranged in a staggered pattern along land portions 114 and grooveportions 115 as shown in FIG. 2(a). Therefore, when reading the CAPAportion 113, the DC level and the amplitude level of the optical disksignals vary rapidly as shown in FIG. 2(b). In order to avoid theinfluence of the level variations, it is necessary to set the acceptableinput amplitude range of the subtracter 23 to be sufficiently large.However, it is undesirable as it leads to an increase in the circuitscale and power consumption.

In view of this, the signal level fixing sections 24 a and 24 b of thewobble signal extraction circuit of the present embodiment fix the inputof the subtracter 23 to a predetermined level within the acceptableinput amplitude range when reading the CAPA portion 113. Specifically,the signal level fixing sections 24 a and 24 b receive a signalindicating the detection of a CAPA portion, and fix the input opticaldisk signals to a predetermined level based on the received signal. Thesignal indicating the detection of a CAPA portion is an essential signalin a DVD-RAM apparatus, and is produced by a circuit other than thoseshown in FIG. 1. This removes the optical disk signals when reading theCAPA portion 113, whereby signals exceeding the acceptable inputamplitude range will not be input to the subtracter 23. Thus, it ispossible to stably extract the wobble signal using, in a DVD-RAMapparatus, a wobble signal extraction circuit that is used in a CD-R/RWapparatus as it is, without setting the acceptable input amplitude rangeof the subtracter to be particularly large.

Note that in a case where the servo system is realized with asample-and-hold method, the function of the signal level fixing sections24 a and 24 b can be realized with a sample-and-hold circuit.Specifically, the sample-and-hold circuit receives a signal indicatingthe detection of a CAPA portion, and holds the input optical disk signalat a predetermined level based on the received signal. Thus, in a casewhere a sample-and-hold method is employed, the function of the signallevel fixing sections 24 a and 24 b is realized without increasing thecircuit scale.

Depending on the type of the optical disk placed in the optical diskapparatus, the function of the signal level fixing sections 24 a and 24b can be disabled for CD-R/RW and enabled for DVD-RAM, whereby it ispossible to provide an optical disk apparatus compatible with bothCD-R/RW and DVD-RAM, wherein the wobble signal can be extracted with asingle wobble signal extraction circuit for any type of optical disk.

Second Embodiment

FIG. 3 shows a configuration of an optical disk apparatus according to asecond embodiment of the present invention. The optical disk apparatusof the present embodiment includes normalizer sections 26 a and 26 bpreceding the subtracter 23 in the optical disk apparatus of the firstembodiment, and further includes gain adjustment sections 27 a and 27 b.The normalizer sections 26 a and 26 b control the amplitudes of theoptical disk signals (A+D) and (B+C), respectively, to be input to thesubtracter 23 to be at a certain level. Then, the subtracter 23calculates the difference between the two normalized optical disksignals, whereby it is possible to suppress the leak of an RF signalinto an extracted wobble signal, thus obtaining desirable wobble signalextraction characteristics.

The signal level fixing sections 24 a and 24 b fix the inputs to thenormalizer sections 26 a and 26 b, respectively, to a predeterminedlevel within the acceptable input amplitude range when reading a CAPAportion. This removes the optical disk signals when reading a CAPAportion. Thus, signals exceeding the acceptable input amplitude rangewill not be input to the normalizer sections 26 a and 26 b. Thus, it ispossible to stably extract the wobble signal using, in a DVD-RAMapparatus, a wobble signal extraction circuit that is used in a CD-R/RWapparatus as it is, without setting the acceptable input amplitude rangeof the normalizer section to be particularly large.

In a case where the inputs to the normalizer sections 26 a and 26 b arefixed to a predetermined level by the signal level fixing sections 24 aand 24 b, if the level becomes near zero, for example, the gains of thenormalizer sections 26 a and 26 b may become maximum and may stay insuch a condition thereafter. In view of this, when the inputs of thenormalizer sections 26 a and 26 b are fixed by the signal level fixingsections 24 a and 24 b to a predetermined level, the gain adjustmentsections 27 a and 27 b fix the gains of the normalizer sections 26 a and26 b to a value used immediately before or to a predetermined value.This suppresses transitional responses of the normalizer sections 26 aand 26 b, thus obtaining desirable transitional response characteristicswhen the read position moves from a CAPA portion into a DATA portion.

Note that the present embodiment is similar to the first embodiment withrespect to the enabling/disabling of the signal level fixing sections 24a and 24 b depending on the type of an optical disk placed in theoptical disk apparatus, and with respect to the realization of thefunction of the signal level fixing sections 24 a and 24 b where theservo system is realized with a sample-and-hold method.

Third Embodiment

FIG. 4 shows a configuration of an optical disk apparatus according to athird embodiment of the present invention. The optical disk apparatus ofthe present embodiment includes the photodetector 20, the adder circuits21 and 22, the subtracter 23, a signal level fixing section 24, thebandpass filter 25 and the normalizer sections 26 a and 26 b. The wobblesignal extraction circuit of the present embodiment is a portionincluding the adder circuits 21 and 22, the subtracter 23, the signallevel fixing section 24, the bandpass filter 25 and the normalizersections 26 a and 26 b.

The signal level fixing section 24 fixes the input to the bandpassfilter 25 to a predetermined level within the acceptable input amplituderange when reading a CAPA portion. This removes the optical disk signalswhen reading a CAPA portion, whereby signals exceeding the acceptableinput amplitude range will not be input to the bandpass filter 25. Thus,it is possible to stably extract the wobble signal using, in a DVD-RAMapparatus, a wobble signal extraction circuit that is used in a CD-R/RWapparatus as it is, without setting the acceptable input amplitude rangeof the bandpass filter to be particularly large.

Note that the present embodiment is similar to the first embodiment withrespect to the enabling/disabling of the signal level fixing section 24depending on the type of an optical disk placed in the optical diskapparatus.

Fourth Embodiment

FIG. 5 shows a configuration of an optical disk apparatus according to afourth embodiment of the present invention. The optical disk apparatusof the present embodiment includes the photodetector 20, the addercircuits 21 and 22, the subtracter 23, the bandpass filter 25, thenormalizer sections 26 a and 26 b and a signal switcher 28. The wobblesignal extraction circuit of the present embodiment is a portionincluding the adder circuits 21 and 22, the subtracter 23, the bandpassfilter 25, the normalizer sections 26 a and 26 b and the signal switcher28.

The subtracter 23 subtracts the output of the signal switcher 28 fromthe output of the normalizer section 26 a. The signal switcher 28outputs the signal from the normalizer section 26 a when reading a CAPAportion, and otherwise outputs the signal from the normalizer section 26b. Therefore, when reading a CAPA portion, the two optical disk signalsinput to the subtracter 23 will be of the same value and thus will becanceled out. This removes the optical disk signals when reading a CAPAportion. Thus, it is possible to stably extract the wobble signal using,in a DVD-RAM apparatus, a wobble signal extraction circuit that is usedin a CD-R/RW apparatus as it is, without setting the acceptable inputamplitude range of the subtracter to be particularly large.

Note that the enabling/disabling of the signal switcher 28 depending onthe

1. A wobble signal extraction circuit for extracting a wobble signalfrom a first optical disk signal containing a wobble signal componentcaused by a wobble formed on a surface of an optical disk and a secondoptical disk signal containing a wobble signal component of a reversedphase to that of the first optical disk signal, comprising: first andsecond signal level fixing sections for fixing the first and secondoptical disk signals, respectively, to a predetermined level when adiscontinuity of the wobble is detected.
 2. The wobble signal extractioncircuit of claim 1, comprising: first and second normalizer sections foradjusting amplitudes of the first and second optical disk signals,respectively, to a predetermined magnitude, wherein the first and secondsignal level fixing sections are provided preceding the first and secondnormalizer sections, respectively.
 3. The wobble signal extractioncircuit of claim 2, comprising: a gain adjustment section for, when thefirst and second optical disk signals are fixed to the predeterminedlevel respectively by the first and second signal level fixing sections,fixing gains of the first and second normalizer sections to a value usedimmediately before the first and second optical disk signals are fixedto the predetermined level, or to a predetermined value.
 4. The wobblesignal extraction circuit of claim 1, wherein: the first and secondsignal level fixing sections perform a sample-and-hold operation on thefirst and second optical disk signals, respectively, and hold the firstand second optical disk signals to the predetermined level when thediscontinuity of the wobble is detected.
 5. A wobble signal extractioncircuit for extracting a wobble signal from a first optical disk signalcontaining a wobble signal component caused by a wobble formed on asurface of an optical disk and a second optical disk signal containing awobble signal component of a reversed phase to that of the first opticaldisk signal, comprising: a subtracter for subtracting the second opticaldisk signal from the first optical disk signal; and a signal levelfixing section for fixing an output signal of the subtracter to apredetermined level when the discontinuity of the wobble is detected. 6.A wobble signal extraction circuit for extracting a wobble signal from afirst optical disk signal containing a wobble signal component caused bya wobble formed on a surface of an optical disk and a second opticaldisk signal containing a wobble signal component of a reversed phase tothat of the first optical disk signal, comprising: a signal switcher forselectively outputting one of the first and second optical disk signals;and a subtracter for subtracting a signal output from the signalswitcher from the first optical disk signal, wherein the signal switcheroutputs the first optical disk signal when the discontinuity of thewobble is detected.
 7. The wobble signal extraction circuit of claim 1,wherein: the optical disk is in compliance with a DVD-RAM standard; andthe discontinuity of the wobble is a CAPA portion.
 8. The wobble signalextraction circuit of claim 1, wherein: the optical disk is incompliance with a DVD-R/RW standard; and the discontinuity of the wobbleis a land pre-pit area.
 9. An optical disk apparatus, comprising thewobble signal extraction circuit of claim
 1. 10. The wobble signalextraction circuit claim 5, wherein: the optical disk is in compliancewith a DVD-RAM standard; and the discontinuity of the wobble is a CAPAportion.
 11. The wobble signal extraction circuit of claim 6, wherein:the optical disk is in compliance with a DVD-RAM standard; and thediscontinuity of the wobble is a CAPA portion.
 12. The wobble signalextraction circuit of claim 5, wherein: the optical disk is incompliance with a DVD-R/RW standard; and the discontinuity of the wobbleis a land pre-pit area.
 13. The wobble signal extraction circuit ofclaim 6, wherein: the optical disk is in compliance with a DVD-R/RWstandard; and the discontinuity of the wobble is a land pre-pit area.14. An optical disk apparatus, comprising the wobble signal extractioncircuit of claim
 5. 15. An optical disk apparatus, comprising the wobblesignal extraction circuit of claim 6.